As a so-called memory card or software card, there is known an optical card 1 in which a plurality of tracks T are formed on a rectangular card substrate in parallel to each other and vertical to its reference end face 1a, as shown in FIG. 1 and information signals are respectively recorded in the respective tracks T by the arrangement of optically recorded loci, for example, pits P as shown in FIG. 2, which can be optically read out.
An optical card reader which reads from such card 1 the information signal recorded on each track T is constructed as shown in FIGS. 3 and 4 such that the card 1 inserted into the reader is transported in the direction shown by an arrow 3 along the reference end face 1a of the card 1 by a card feed roller 2, a light 5 from an irradiating light source 4 such as a light-emission diode is introduced onto the track T of the card 1 through a condenser lens 6, a reflected light from the track T, that is, a reading light 7 of the track T is projected through a focusing lens 8 to a photo detecting element 10 supported on a support plate 9 and the reflected light is detected by this photo detecting element 10. The photo detecting element 10 is constructed just like a line sensor made of a CCD (charge coupled device) such that a plurality of photo detecting elements 10a are arranged rectilinearly and the images projected thereon are read out by the electrical scanning. As shown in FIG. 5, on the photo detecting element 10, the longitudinal direction of the image of the track coincides with the arrangement direction of the detecting elements 10a, whereby images P' of all pits on one track are simultaneously focused on the photo detecting element 10 and thus the informations of one track amount can be read at a time.
The electrical arrangement of the prior art optical card reader is as shown, for example, in FIG. 6. As shown in the figure, the photo detecting element 10 is so formed that a plurality of light receiving elements 10r and transfer elements 10t corresponding to the former one by one are respectively located in opposing relation across a gate 10g.
First, the gate 10g is closed during a predetermined period (accumulation period) so that the charge produced by the light is accumulated in each of the light receiving elements 10r. Then, the gate 10g is opened momentarily to transfer the accumulated charges to the corresponding transfer elements 10t in parallel to one another, respectively. Also, the accumulation of the charges is started again in the light receiving elements 10r. The charges transferred to the respective transfer elements 10t are scanned by a scanning signal (read clock) from a scanning circuit 31 and then read out as a series signal during a constant period (scanning period).
Since the accumulation period and the scanning period are same in time period and timing, the term of the scanning period (scanning) will be used in the following explanation.
The read-out signal, which is the output from the photo detecting element 10, is a discrete analog signal produced at the unit of the detecting element 10a. This signal is amplified to a predetermined level by an amplifier 32 and converted through a sample and hold circuit 33 and a low pass filter 34 to a successive analog signal which is then supplied to a comparator 35. The signal inputted to the comparator 35 is converted to a binary coded signal on the basis of the fact that the voltage thereof is higher than or lower than a reference voltage. The read-out and binary coded signal is supplied to a PLL 36 and a data reproducing circuit 37. In the PLL 36, a clock signal is extracted and then reproduced from the read-out signal and this clock signal is supplied to the data reproducing circuit 37 by which the binary coded data is reproduced. The binary coded data reproduced is supplied to a data processing circuit 38 in which it is processed properly by using the clock signal from the PLL 36.
As an optical card, there is known such one in which an optically readable mark (track mark) is formed at the position corresponding to each of the tracks, whereby it is possible to know the address of the track to be read by using this mark M and an arbitrary track can be selected and then read out.
FIG. 7 illustrates one example of such optical card, in which a plurality of parallel tracks T are formed on a rectangular card substrate vertical to its reference end face 11a, an information signal is recorded on each of the tracks T by the arrangement of the pits so as to be optically readable as mentioned before and a rectilinear mark M of straight line-shape is formed in parallel to each of the tracks T at the position on the extension above each of the respective tracks T. This mark M is made to be optically readable. For example, when the reflectivity of light in the pit portion of the track T is selected to be low as compared with other portion, the reflectivity of the mark M is also selected to be low. On the contrary, when the reflectivity of light in the pit portion of the track T is selected to be high as compared with other portion, the reflectivity of the mark M is also selected to be high.
FIG. 8 shows one example of a photo detecting element used in a reader applied to such an optical card. A photo detecting element 20 supported on a support plate 19 is formed of a photo detecting element 21 which reads a track T on a card 11 and a photo detecting element 22 located at the upper side thereof. The photo detecting element 21 is such one in which a plurality of detecting elements 21a are arranged rectilinearly similar to the afore-mentioned photo detecting element 10 and also the photo detecting element 22 is formed by arranging a plurality of detecting elements 22a rectilinearly. However, the photo detecting element 22 is constructed such that the sum of the outputs from the plurality of detecting factors 22a is delivered as the output of the photo detecting element 22.
Though not shown, the optical system of such reader is constructed such that a light from an irradiating light source is introduced into the card 11 so as to have the length not only corresponding to the length of the track T of the card 11 in FIG. 7 but also extending to the length of the mark M, the light for reading the mark M in FIG. 7 is projected onto the photo detecting element 22 and the light for reading the track T is projected onto the photo detecting element 21.
The electrical construction of the prior art optical card reader is as shown, for example, in FIG. 9 and as shown in the figure, the photo detecting elements 21 and 22 are formed such that a plurality of light receiving elements 21r and 22r and transfer elements 21t and 22t corresponding to the former one by one are located across a gate g, respectively.
At first, the gate g is closed during a contant period (accumulation period) and the charges generated by the light are accumulated in the respective light receiving elements 21r and 22r. Then, the gate g is momentarily opened to transfer the accumulated charges to the corresponding transfer elements 21t and 22t in parallel to one another and the accumulation of charges in the light receiving elements 21r and 22r is started again. The charges transferred to the respective transfer elements 21t and 22t are scanned by a scanning signal (a read clock) from a scanning circuit 31 and are read out as a series signal during a constant period (scanning period).
The read-out signal as an output of the photo detecting element 21 is a discrete analog signal generated at the unit of the detection elements 21a. It is amplified to a predetermined level by an amplifier 32, supplied through a sample and hold circuit 33 and a low pass filter 34 so as to be made as a successive analog signal and then fed to a comparator 35. The input signal to the comparator 35 is converted to a binary coded signal on the basis of the comparison that the voltage thereof is higher or lower than a reference voltage. The binary coded read out signal is supplied to a PLL 36 and a data reproducing circuit 37. In the PLL 36, a clock signal is extracted and reproduced from the read-out signal and the resulting clock signal is supplied to the data reproducing circuit 37 which reproduces the binary coded data. The binary coded data thus reproduced is supplied through a gate 39 to a data processing circuit 38 in which it is properly processed by using the clock signal from the PLL 36.
The track mark detecting signal, which is an output from the track mark photo detecting element 22, is supplied through an amplifier 23 to the gate 39 and thereby the gate is opened so that the data reproduced by the data reproducing circuit 37 is transferred to the data processing circuit 38 only when it is the information of the track.
As described before, upon reading, the optical card is transported in the direction perpendicular to the track and the images of the respective tracks projected onto the photo detecting elements are read out by the electrical scanning.
Here, three pits P1, P2 and P3 belonging to adjacent arbitrary three tracks and aligned along the card transportation direction 3 as shown in FIG. 10 will be considered. The incident light amounts onto the particular photo detecting elements corresponding to the pits P1 to P3 are periodically changed in response to the transportation of the card as shown in FIG. 11. In other words, the incident light amounts become maximum at time points tc1, tc2 and tc3 at which the centers of the projected images of the pits P1, P2 and P3 coincide with the centers of the photo detecting elements. While, they become minimum at time points at which the intermediate portions between the respective pits are projected onto the photo detecting elements, in other words, at intermediate time points tm1 between the time points tc1 and tc2 and tm2 between the time points tc2 and tc3.
However, the scanning period of the track to which the pit P2 belongs falls in a range between the two time points tm1 and tm2 at which the photo detection outputs become minimum across the time point tc2 at which the photo detection outputs become maximum. So, the read-out signal obtained from the photo detecting elements contain an invalid component which is provided by the projected image on the intermediate portion between the adjacent tracks. There is then a problem that a contrast of a pit corresponding signal by the projected image of the pit will be deteriorated.
When the scanning timing is displaced by any cause and then the scanning period becomes from tc1 to tc2 or from tc2 to tc3, the informations recorded on the two tracks are read out simultaneously or such a state equivalent to a case in which the two tracks are superposed is presented. Thus, a correct information can not be read. Further, even in the case of the optical card provided with the track mark M as shown in FIG. 7, when the scanning timing is displaced by any cause and the scanning period becomes from tc1 to tc2 or from tc2 to tc3, the output from the track mark detecting element 22 becomes the same as that obtained when the scanning timing is the normal one so that the gate 39 is opened. Thus, the informations recorded on the two tracks can be read out simultaneously with the problem that the correct information can not be read out, too.
In view of the above aspect, an object of this invention is to provide an optical card reader which can increase the contrast of the signal corresponding to the optically recorded loci and correctly and stably read the information recorded.